Device for opening and closing electrical circuits



y 1961 w. E. SINNER 2,982,884

DEVICE FOR OPENING AND CLOSING ELECTRICAL CIRCUITS Filed March 7, 1956 40 a E M o: M Q

IN V EN TOR.

WOODROW EUGENE SINNER DEVICE FOR OPENING AND CLOSING ELECTRICAL CIRCUITS Woodrow Eugene Sinner, Des Moines, Iowa, assignor to Bjorksten Research Laboratories Inc., Fitchburg, WIS. a corporation of Illinois Filed Mar. 7, 1956, Ser. No. 570,131

1 Claim. (Cl. 317-141) The present invention relates to electrical apparatus and in particular to devices for opening and closing electrical circuits.

Control circuits designed to be responsive to temperature, pressure, height of fluids, rates of flow, and a host of other physical parameters require that a circuit be frequently closed and after a suitable period be opened. When the sensing means is responsive to change in the physical parameter above and below some predetermined constant value, such as is encountered in a thermostat or a device to maintain constant pressure in a tank, or a device to maintain a constant level of water in a tank, the electrical contacts in the control circuit which close and open the control circuit are held very close together though not touching for extended periods prior to closing and subsequent to opening of the circuit. Such juxtaposing causes arcing across the contacts and resonate closing and opening of the circuit. Arcing and unnecessarily frequent opening and closing of the circuit causes rapid pitting of the contacts necessitating their frequent replacement. Resonate opening and closing of the control circuit is termed hunting; the contacts may be described as chattering when such resonate phenomena are present.

One object of the present invention is to provide an apparatus for opening and closing a circuit adapted to suppress short period resonance in a control circuit.

Another object of the present invention is to provide a contact locking device adapted to be unresponsive to fleeting juxtaposing of the contacts and adapted to hold the contacts locked together despite fleeting interruptions in the closed circuit.

These and other objects and advantages of my invention will be apparent from the following specification, claim and drawing.

My invention comprises briefly an improved apparatus for opening and closing a first electrical circuit having a fixed soft-iron contact and a movable iron contact, the improvement therein comprising a second circuit in parallel connection with the two contacts, the second circuit being provided with an electromagnetic coil, a capacitance, a rectifier, and voltage regulation means, the electro-magnetic coil being disposed to induce a magnetic field in the fixed soft iron contact in response to closing the first circuit, the capacitance in the second circuit being adapted to delay the response of the magnetic field to opening and closing of the first circui the voltage regulation means being adapted to regulate the intensity of the magnetic field holding the contacts together, whereby the contacts of the first circuit are held firmly together under the influence of the magnetic field after a briefly sustained contact, and are separated by a briefly sustained external force adapted to momentarily hold the contacts apart.

The figure is a schematic partially perspective view of my invention adapted for use in a thermostat control circuit showing the circuits and fragments of necessary mechanical components.

Patented May 2, 1961 ice Referring now to the figure, a temperature-sensitive bimetal 10 is held rigidly at one end 12 by a base 14; the opposite end 16 of the bimetal 10 is free to move in response to variation in ambient temperature. Two soft iron contacts 18 and 20' are held rigidly with respect to the base 14. The free end 16 of the bimetal carries movable contacts 22 and 24. When the bimetal 10 is subjected to temperature variation it flexes, causing the contact tip 22 to approach and contact the fixed contact 18, or in the event of a temperature change of opposite sign the contact 24 is caused to approach and contact the contact 20. The thermostat control circuit derives power from a main 26 and upon closing the circuit as described above, transmits an electrical signal to load 50 or 52. The voltage supplied at 26 may he stepped down from line voltage by a transformer which for simplicity is not shown and voltage supplied to either or both of loads 50 and 52 may be stepped up likewise by transformers which for simplicity are not shown.

The auxiliary circuits described below contribute the resonance damping and contact lock-in features of my invention. Electromagnetic coils 32 and 34 are disposed about the soft iron contacts 18 and 20 respectively, and are adapted to induce a magnetic field within the contacts 18 or 20 of sufiicient intensity to hold the contact points 18 and 22 or 20 and 24 respectively locked in firm electrical contact. The intensity of the magnetic fields may be regulated by the voltage regulation means 36 and 38 comprised of variable resistance elements in series connection with the coils 32 and 34 respectively. The electromagnetic coils 32 and 34 respectively are powered by direct current derived from rectifiers 40 and 42 connected in parallel with the contacts 22, 18 and 20, 24 of the main control circuit. The rectifiers 40 and 42 are placed in series with the electromagnetic coils 32 and 34 in the auxiliary circuit. Condensers 44 and 46 are connected, within the auxiliary circuits, with the coils 32 and 34 respectively. The condensers 44 and 46 are adapted to delay for a brief interval the formation or the collapse of the magnetic fields in the contacts 18 and 20 in response to closing the main circuit.

The iron contacts may have their contacting surfaces provided with a layer of arc-resistant material such as silver or the like which may be applied by dipping, soldering or any suitable method. For simplicity, such layers are not shown. Ferromagnetic armatures and cores may also be used for purposes of the invention which are spaced apart from contacts of arc-resistant material.

Operation of my inventive apparatus will now be described. When the main control circuit is closed by flexing of the bimetal 10 which brings the contacts 18 and 22 into juxta-position, a current fiows through the auxiliary circuit powered by the output of the rectifier 40. The amount of current caused to flow through the auxiliary circuit is regulated by adjusting the variable resistance 36. The condenser 44 is charged, thereby delaying energizing .the electromagnetic coil 32 and delaying the formation of a magnetic field in and about contact 18. If the contacts 22 and 18 are held closed for a sufficient period of time, which time interval may be arbitrarily selected from between V seconds to 15 seconds or longer, the condenser 44 will be charged, current Will flow through the coil 32 and the contacts will be held firmly locked together by the magnetic field. Upon breaking the circuit, the magnetic field will be sustained for a brief interval while current flows out of the condenser 44 and through the coil 32; thus it the contacts are only momentarily separated, the magnetic lock-in will not be interrupted. Therefore, as the bimetal relaxes the force holding the contacts together, the contacts cannot separate sufficiently to cause arcing or chatter. The main circuit may be opened only upon application of a sustained force separating the contacts for a predetermined period; such a period may be selected between of a second and 15 seconds or longer. Op- :eration of the auxiliary circuit adapted to magnetize the iron contact 20 is analogous in all respects to the operation of the circuit described above pertaining to contact 18. a t

It is intended that my invention not be limited by the embodiment described above but only by the following claim.

i I claim: a

An improved apparatus for opening and closing a fixed ferromagnetic contact and a movable ferromagnetic contact in a main electrical circuit, the improvement comprising an auxiliary circuit having an electromagnetic coil disposed about the fixed contact, a condenser connected in parallel with the coil and adapted to delay the response of the magnetic field to opening and closing the circuit, a resistor within the auxiliary circuit in series with the coil, a four terminal rectifier having two terminals connected across the main electrical circuit, and two 5 terminals connected to power the auxiliary' circuit.

References Cited the file of this patent UNITED STATES PATENTS 10 2,016,144 Hill Oct. 1, 1935 2,210,669 Johnson Aug. 6, 1940 2,320,208 Wurth May 25, 1943 2,373,202 Snell Apr. 10, 1945 2,440,108 Maxwell Apr. 20, 1948 15 2,572,598 Curtis Oct. 23, 1951 FOREIGN PATENTS 603,981 Great Britain June 25, 1948 

